This SBIR application proposes to pre-clinically evaluate a pDNA prime - rVSV boost HCV vaccine intended to improve the sustained virologic response (SVR) rate in patients being treated with current standard of care (SOC) therapy for chronic HCV infection. Of the approaches being developed as candidate vaccines, those based on priming with pDNA followed by boosting with a live recombinant viral vector such as vesicular stomatitis virus have proven to be the most immunogenic. Preliminary results demonstrate that non-human primates (NHPs) which receive HIV pDNA prime - HIV rVSV boost mount a significantly more robust response than do macaques receiving pDNA prime - pDNA boost (p<0.05). In addition, the vaccination strategy proposed in this application has been designed specifically to overcome the immunologic anergy that characterizes chronic HCV infection. Multiple studies have now demonstrated that immunization with pDNA vaccines is effective in the induction of antigen- specific central memory (CM) T cells that exhibit both long-term persistence in vivo and a high expansion potential. These CM T cells do not show up-regulated expression of PD-1, CTLA-4, and LAG-3, making them resistant to a range of negative regulatory mechanisms. Second, IL-12 is known to up regulate CD28 and CD127 expression on T cells and to be a potent inhibitor of tolerance induction. The pDNA prime/rVSV boost HCV vaccine proposed in this application incorporates a clinically validated IL-12 expression plasmid in the pDNA priming component, and the VSV boosting vector is a potent stimulator of IL-12 production. This phase I application proposes to conduct an enabling trial in NHPs to: ( Confirm the immunogenicity of the pDNA and rVSV vectors in a higher species. ( Confirm that co-administration of IL-12 pDNA improves the magnitude, breadth, poly-functional nature, and tolerance resistance of the HCV-specific CMI response. ( Determine if PEG-IFN administration to patients undergoing SOC treatment will need to be paused at the time of rVSV booster vaccination. PUBLIC HEALTH RELEVANCE: This SBIR application proposes to pre-clinically evaluate a hepatitis C virus vaccine intended to improve the cure rate in patients being treated with drugs for chronic HCV infection. Surveillance studies conducted by the Centers for Disease Control and Prevention (CDCP) and the NIH show that HCV accounts for 40% to 60% of chronic liver disease in the US and that chronic liver disease is currently the tenth leading cause of death among adults. HCV is the most frequent indication for liver transplantation in US; the number of patients on transplant waiting lists has doubled in the past 5 years, and about 50 percent of these patients die while awaiting an organ.